Michaela Whitbourn, Kate McClymont

Bart Bassett has become the ninth state Liberal MP to join the crossbench after a corruption inquiry into illegal donations was formally widened to examine allegations that Nathan Tinkler's property development company improperly sought to influence him over a housing development.

Mr Bassett, a former mayor and the member for the seat of Londonderry in western Sydney, announced on Wednesday afternoon that he would "stand aside" from the parliamentary Liberal Party during the inquiry.

Mr Bassett joins six of his colleagues on the crossbench, including former ministers Mike Gallacher and Chris Hartcher. Another two MPs, Tim Owen and Andrew Cornwell, have since resigned.

Including Barry O'Farrell, who resigned as premier amid a separate inquiry earlier this year, almost 16 per cent of the parliamentary Liberal Party has been embroiled in the state's growing corruption saga.

ICAC heard on Wednesday that Mr Tinkler's company Buildev made an illegal $18,000 payment to Mr Bassett's election campaign for the seat of Londonderry in December 2010.

The commission heard the $18,000 was paid to an alleged Liberal Party front organisation called the Free Enterprise Foundation. It "went straight into Mr Bassett's [election campaign] account" and was used to buy election advertising material.

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Property developers have been banned from making political donations in NSW since 2009.

"Do you think a payment could have been made into that election account as a way of thanking Mr Bassett for decisions he'd made to benefit Buildev?" counsel assisting, Geoffrey Watson, SC, asked Buildev co-founder Darren Williams.

"You could make that speculation," Mr Williams replied. "It's not my recollection."

Asked whether the money was paid with a view to influencing Mr Bassett to make decisions which could assist Buildev, Mr Williams said: "You could speculate that."

ICAC heard that Buildev executives met Mr Bassett, then Hawkesbury mayor, at his home in May 2007.

"We can land [the Buildev helicopter] at his house, more private," Buildev development partner Mark Regent wrote in an email.

Mr Regent said in a January 2007 email – before laws were passed banning donations from developers – that Mr Bassett had been "great" and the company needed to pay him a donation.

Buildev's employment of the dark arts of political manipulation were revealed in a series of texts and emails tendered at the inquiry.

ICAC has heard that Buildev executives did their utmost to sideline critics of their controversial housing project in North Richmond.

In 2007, Buildev executives discussed hiring a local solicitor to "advise" on their project. This would mean that his wife, a local councillor, would not be able to vote on the matter because of a conflict of interest. They also discussed hiring people to fill out submissions supporting their North Richmond project.

Mr Williams also discussed approaching the head office of the NSW Labor Party to put pressure on ALP politicians who were against the Buildev project. "We will see Mark Arbib and Eric Rossendal [sic]" read an email from Mr Williams on May 29, 2007.

Mr Williams denied that donations were a way of buying influence. "You don't buy influence, you buy the ability to put your case forward," Mr Williams said. He complained that otherwise "you can wait months" to see your local MP.

Due to boundary changes in his seat of Londonderry, Mr Bassett has been trying to find another seat to contest at the 2015 election, but the allegations aired at ICAC are likely to cruel his chances.